This can be done but you would need to write a rather advanced Photon program to do this. There are a number of complications such as how to move the pointer effectively using the keyboard. Moving one pixel per keystroke would be too slow, but not having fine control would make operating the system impossible. You also have to figure a way to pass through the keys you use for cursor control when the program needs to see them.

Does this have to allow 'free-play' in that the mouse can move anywhere and do drag-drop, resizing, right clicks etc? Or do you have fixed objects (buttons, icons etc) that you just want the user to be able to easily jump from one to another to select one?

If it's the latter, you can just let the Tab key cycle between your buttons/objects and have the Enter key select (left mouse click). In the mid 90's under QNX Windows I did that on a system that had a keyboard and no mouse. I also had a 1 letter short cut for all my buttons (that 1 letter was a different color than the other text in the button so users would know what the shortcut was for any button) so that the Tab cycling wasn't necessary.